When a woman gets pregnant, there is usually excitement, joy … and sometimes a little concern that the baby will be born healthy. One reason for this concern is the possibility of having a child with Down syndrome, a lifelong genetic disorder that affects development both in the womb and after birth.

Down syndrome is one of the most common genetic disorders in the U.S.; each year about 6,000 babies are born with the condition.

Most people with Down syndrome have mild to moderate impairments throughout life. There are some common physical traits in people with Down syndrome, including a flatter facial profile, eyes that slant upward, low muscle tone, smaller hands and feet, one crease across the palm, a short neck, small ears and a small mouth.

Here are some facts to know about Down syndrome.

1. The most common type of Down syndrome is called Trisomy 21

Down syndrome is a genetic birth defect. Typically, each cell in the human body contains 23 pairs of chromosomes that carry genetic information from both parents.

About 95 percent of people with Down syndrome have an extra copy of chromosome 21, for a total of 47 chromosomes. This type of Down syndrome is called Trisomy 21.

There are two other types of Down syndrome: Mosaicism, where only some cells contain 47 chromosomes and others contain 46; and translocation, where there are 46 chromosomes present, but chromosome 21 attaches to another chromosome.

2. No one knows what causes Down syndrome

Researchers are unsure why Down syndrome occurs or all the factors which increase the risk. However, one factor is the mother’s age.

“A 35-year-old woman has a 1 in 350 chance of giving birth to a baby with Down syndrome,” said Murugu Manickam, M.D., clinical geneticist at Geisinger Health System’s Genomic Medicine Institute Precision Health Center in Forty Fort. “This increases each year. By age 40, the chance of Down syndrome is 1 in 100. Overall that risk could be considered low but it is higher.” However because of normal childbearing ages, most children with Down syndrome are born to mothers who are less than 35.

Having had another child with Down syndrome is also a risk factor.

3. Down syndrome may be diagnosed before or after the baby is born

During pregnancy, a noninvasive blood screening test can determine if you are more or less likely to have a baby with Down syndrome.

If screening tests are positive, your doctor may recommend a more invasive diagnostic procedure to determine whether or not your baby has Down syndrome. These tests look for differences in chromosomes that signify Down syndrome.

After birth, Down syndrome may be identified by appearance and confirmed with a test called a karyotype.

4. Some people with Down syndrome may have other health issues

Babies born with Down syndrome often face other birth defects.

“About half of babies born with Down syndrome also have heart problems that could require surgery or close monitoring,” said Dr. Manickam.

Other health issues include hearing problems, sleep apnea, seizures, skin conditions, vision problems, digestive issues, respiratory infections and gum disease. As people with Down syndrome age, their related health problems may worsen.

5. People with Down syndrome are living longer than ever before

Thanks to early diagnosis and advances in treatment, the life expectancy of people with Down syndrome has increased significantly.

“As recently as 1983, the average life expectancy was around 25 years old,” said Dr. Manickam. “Now, many people with Down syndrome live very full lives into their 60s and sometimes 70s.”

It is also very important to talk to other families who have a child or adult with Down syndrome. There are numerous local and national organizations that can help connect families, Dr. Manickam said.